The present invention relates to a technique for controlling a control duty ratio which determines a magnitude of voltage to be applied to a motor mounted on an electric power tool.
Upon accelerating a motor of which rotation is in a stopped state, it is desirable that the rotation speed of the motor is quickly increased.
In Unexamined Japanese Patent Application Publication No. 7-039181, upon accelerating a motor of which rotation is in a stopped state, a duty ratio of a voltage applied to the motor is set high if a target rotation speed of the motor is high, and the duty ratio is set low if the target rotation speed is low.
When the target rotation speed is high, the duty ratio is set higher than the duty ratio when the target rotation speed is low. Thus, the rotation speed of the motor quickly goes up to rapidly reach the target rotation speed. On the other hand, when the target rotation speed is low, the duty ratio is set low. Thereby the rotation speed can reach the target rotation speed, while avoiding overshooting the target rotation speed.
As above, motor control that, upon accelerating the motor of which rotation is in a stopped state, increases the rotation speed of the motor by adjusting the duty ratio of the voltage applied to the motor can be applied to an electric power tool having a motor as a drive source.